Ebola and Marburg viruses belong to the family Filoviridae and can cause fatal hemorrhagic fevers characterized by widespread tissue destruction with an incubation period of 4-14 days. Because of the safety concerns, these viruses are designated as the biosafety level 4 agents. Progress in elucidation of the mechanisms of filoviral entry and pathogenesis has been hampered partly due to the safety concern. Currently there is no effective vaccine or therapeutic treatment against filoviral infection and pathogenesis in human. Further, it may never be entirely practical or desirable to vaccinate large portions of the population against this disease due to the facts that the minimal time required for vaccination is at least one month and that the filoviral outbreaks are sporadic in nature. Thus it is imperative to identify and develop potent inhibitors against filoviral infection. In this application, we demonstrate that Ebola glycoproteins (GP) can be efficiently incorporated onto HIV viral particles, and the pseudotyped virions can mediate efficent viral entry. More importantly, in the preliminary experiments, we have shown that this system can be used as a powerful assay to screen and identify molecules that can block Ebola entry to the target cells. The overall objective of this application is to screen and develop molecules which can specifically inhibit Ebola viral entry. This application will focus on the following three specific aims: (1) Optimization of lead compounds by iterative synthetic chemistry. (2)Screening and identification of small compounds which inhibit Ebola entry using high throughput screenings (HTS). And (3) Validation and development of Ebola entry inhibitors. These studies should identify and develop potent entry inhibitors against Ebola viral infection and disease. Summary In the original proposal "Screening and development of anti-Ebola entry inhibitors" (NIH UO1 AI77767- 01), we proposed three specific aims: (1). Optimization of the lead compounds by iterative synthetic chemistry, (2). Screening and identification of small compounds that inhibit Ebola entry, and (3). Validation and development of Ebola entry inhibitors. Since we proposed the five years of research plan in the original application, we now wish to modify the scope of the original application to reflect the shorter duration of the application (two years instead of five years). Here we will highlight the proposed major modifications in the current application and these changes will be elaborated in the following sections: 1. The current application will have the same three specific aims as stated in the original application (see above), but the proposed experiments will be more focused to reflect the shorter duration of the research plan. 2. In the original application, we proposed to test a series of Ebola entry inhibitors using animal models. However, we believe that it is highly unlikely that animal experiments as originally proposed will be performed during a two-year period. We request to remove that part of the proposed experiments altogether, and the subcontract of $75,000/per year for Dr. Viktor Volchkov's group in France. Therefore no animal protocol is needed for the current application. 3. In the original application, we proposed to test and validate the most promising entry inhibitors using infectious Ebola virus in a BSL-4 facility (Aim 3). These experiments are important in the current application, and they will be performed in collaboration with Drs. Lisa Hensley and Gene Olinger at USAMRIID. We have set up a collaboration agreement with these Ebola research experts (see the attached agreement). However, we do not request any budget for this part of work since Drs. Hansley and Olinger have other financial supports to carry out the proposed experiments. It is important to emphasize that due to its highly pathogenic nature to humans, Ebola virus is considered a serious public health threat, and it is an integral part in the US HHS Public Health Emergency Medical Contermeansures Enterprise Strategy (HHS PHEMCE Strategy, Federal Register, 2007, 72(53), 13109- 13114). Therefore, the current application has great implications for the national security. 1